grid, generator and solar battery backup

[synchro]

This is describing the operation of a PV assist generator supply system to a large commercial load. These have been around for a while and do not apply to the standard residential load. They require that the generator be sized to supply 100% of the load when in backup mode and that the PV system is sized to no more than 35% of the load. The load cannot be allowed to drop below the level of the PV system output, which is why the PV output is limited. If it does the generator and PV system will be damaged. So the load needs to have a high minimum value during any time the PV system is in production. These can be made to work where the load has a constant high demand but that's not usually a residential system.

I think another limitation with connecting grid-tie inverters to a generator is that these inverters rely on the grid impedance to be very low so that it maintains a relatively clean voltage waveform in the presence of distortion in the PWM output current of the inverter. The higher the impedance of the source, the more distortion voltage will be developed for a given level of distortion current. Too much voltage distortion can adversely affect loads such as lighting, electronics, etc. An oversized generator will have a lower impedance and therefore result in a lower level of voltage distortion, but even so the impedance will very likely be larger than that from the POCO service. Passive and active filtering techniques could reduce the amount of inverter output current distortion, but that comes at a cost.
As others have said, incorporating an ESS eliminates a number of constraints and adds a lot of capability. Also it allows the generator to be run at higher loading levels where the engine is more efficient and then shut off when the ESS and PV can take over.

 

[caribconsult]

I would have a switch at the entry point to main house panel that allows you to switch from Tesla to the Generator. Don't cross-connect these two. One or the other to the house. You can leave the grid on to gateway or not, it doesn't matter. The Tesla will charge from the panels and go into idle mode until you switch off the grid and revert to the Tesla with this switch. We have this and it works perfectly. And this way you can pull the entire capacity of your generator service, not limited to ~5Kw of the PW.

 

[caribconsult]

There is a way to fire up the Tesla using your gen, if the grid isn't available. You'll need a 115vac to 12vdc power supply and you should have a pretty charge in the PW at that point. Fire up the gen, connect the 12 VDC supply to 115VAC. Remove the interior front cover panel on the Tesla gateway (I only speak of Tesla gear here) and look down at the lower left corner and you'll see several light green terminal strips including one labeled 'JUMP' showing polarity. Using the 12v power supply, connect both the POS and NEG with some test leads from the power supply to the correct polarity terminals and the light in the PW should start blinking. This is best done in the day time when the pv array and inverters are live, and where you have a good view of the light on the PW as well as access to the gateway. When the PW light stops blinking and remains on, remove the 12v leads and let it finish firing up. If there's some sun, it might put some charge in your battery too. As soon as the grid returns, let that bring you back to full charge. Be careful inside the gateway...there's live 240+VAC in there and you could get quite a jolt so don't touch anything but the terminal strip. Be sure to replace the interior front cover when done. And kill anything unnecessary until the battery has some charge, like 50%. Alternatively, you could just switch the house to run on the gen only and wait for some sun...the Tesla might restart itself once the panels are producing.

 

[tortuga]

Call me old school but I see no need for a packaged ESS product, to take a typical 'grid tie' residential system and convert it go a generator / backup system just use a sunny island and some batteries. The sunny island provides the sync for the 'grid tie' inverters.

 

[Carultch]

Call me old school but I see no need for a packaged ESS product, to take a typical 'grid tie' residential system and convert it go a generator / backup system just use a sunny island and some batteries. The sunny island provides the sync for the 'grid tie' inverters.

There are other advantages to packaged ESS products, that the sunny island system doesn't have. The newer ESS solutions work with a higher battery voltage, and battery systems that occupy less space, unlike the Sunny Island system that was built for a day when battery banks were limited to 48V.

 

[tortuga]

There are other advantages to packaged ESS products, that the sunny island system doesn't have. The newer ESS solutions work with a higher battery voltage, and battery systems that occupy less space, unlike the Sunny Island system that was built for a day when battery banks were limited to 48V.

Aww now thats interesting. I like to turn tools and get hands on, so I like having lots of options.
I am really resistant to the idea of a ESS 'product' and now it has to be listed.

The general level of packaging stuff together the PV sales industry does is contrary of the electrical industry tradition of interoperability (and more like plumbing).
It still bugs me that to replace most resi inverters I have to handle live 480VDC or go up on a roof because the disconnect is 'integrated for labor savings'.
But if I need to replace a heatpump compressor I can just pull the disconnect located adjacent to the machine.
If I buy a steel city box I can put a leviton receptacle in it. Solar not the case, lots of brand lock in.
I like being able to mix and match brands.
An ideal inverter to me would be just like a ACME transformer, a grey box with nothing much else, you add disco's whatever where ever you need.
Same with the charge controller.
Inverter + charge controller and throw in some used EV batteries together and you have an ESS for a fraction of the price.


The 48V is not a deal breaker when compared with the simplicity of the setup but its pretty bad ill agree, I personally think article 706 should be deleted, article 480 is fine the way it is or at least get rid of that bizarre 100VDC limit in 706.20(B) and change it to a standard 120VDC.
Just my two cents...

Sunny island specs:

https://files.sma.de/downloads/SI6048US-DS-en-27.pdf

 

[jaggedben]

Call me old school but I see no need for a packaged ESS product, to take a typical 'grid tie' residential system and convert it go a generator / backup system just use a sunny island and some batteries. The sunny island provides the sync for the 'grid tie' inverters.

In my opinion Powerwall and Enphase Ensemble are an improvement over Sunny Island in all areas.

 

[tortuga]

In my opinion Powerwall and Enphase Ensemble are an improvement over Sunny Island in all areas.

Yeah every product has a customer, i am glad there are all these options, we install whatever people want.

Its just my preference to have more interchangeable components.
I just picked up a 2019 'Generation 3' Nissan leaf battery pack.
I am going to take 35 cells from it and make a 22kw battery pack for under $4000.
Its just more my style.

The only thing I get really insistent about in the design phase is my design rule #2;
Permanently installed electrical products that require network acces to properly function shall use 'wired ethernet'.

Not that that happens though, but corporate security / government types like my input more than homeowners.
Its a pain to have to drive an hour to a customers house just to find out the problem is their teenage kid changes the wifi password.
Or to find out someone unlocked your building back door after they uploaded malware to the network by exploiting a open port on a WIFI connected 'smart' PV electrical device.
Cheers

 

[david056]

There are two options for this:
Option 1: use an ESS that supports a generator. Sonnen does. Enphase will soon. Even older technology like the Conext XW will do it although it's the opposite of user friendly. Also Sunny Island as mentioned, but like the Context that's becoming somewhat obsolete in my opinion. There are others.

Option 2: put an ATS between the ESS and the backup loads panel. But this precludes recharging the ESS with the generator, and may have other difficulties with ATS operation (depending on ESS off-grid switchover time) and pass through amperage.

 

[david056]

There are two options for this:
Option 1: use an ESS that supports a generator off grid. Sonnen does. Enphase will soon. Even older technology like the Conext XW will do it although it's the opposite of user friendly. Also Sunny Island as mentioned, but like the Context that's becoming somewhat obsolete in my opinion. There are others.

Option 2: put an ATS between the ESS and the backup loads panel. But this precludes recharging the ESS with the generator, and may have other difficulties with ATS operation (depending on ESS off-grid switchover time) and pass through amperage.

This will also help you out
Just install a battery/inverter(ESS) that supports a generator, like Sonnen. Simple